This invention relates to a core used in the formation of, for example, a tire such as disclosed in U.S. Pat. No. 3,606,921 to C. E. Grawey issued Sept. 21, 1971.
U.S. Pat. No. 3,883,287 to Grawey et al issued May 13, 1975 (assigned to the assignee of this invention), discloses apparatus including a rigid mold body and an expandable bladder associated therewith, the bladder being inflatable and expandable to form and press a core between itself and the mold body. Such core is made up of sand core material and an annular substantially inextensible roll-restraining hoop. The roll-restraining hoop as disclosed in that patent defines in cross-section a rounded upper end. In the final core as formed, a side surface of the roll-restraining hoop defines a portion of the outer surface of the core.
In general, the roll-restraining hoop of the type disclosed in that patent is made up of a first elastomeric annular part having substantially inextensible wires embedded therein, and a second annular part of elastomeric material secured to the first part. The elastomeric materials making up the separate roll-restraining hoop portions are uncured and are joined together as a unit to form the overall roll-restraining hoop. The hoop is then located within the upper portion of the mold, as described in that patent.
As is well known, all rubber materials, whether cured or uncured, tend to assume an original form when released from an applied stress. In the presently used system as disclosed in that patent, a great degree of care must be exercised in the operation joining the roll-restraining hoop sections, to provide proper relative positioning of those portions. This is extremely important since one side of the roll-restraining hoop defines a portion of the outer surface of the core, and it is of great interest that this outer surface of the core be smooth and continuous throughout. Reference will be made herein to particular problems which may result in the above system.